1. Field of the Invention
The present invention relates to a functional metallic material, especially relates to a metallic material showing a shape memory effect and a pseudo-elasticity.
2. Description of the Prior Art
Shape memory alloys have a possibility for being applied to various fields such as industry, energy, medical science by utilizing its unique facility, and these alloys are utilized in those fields. The shape memory effect and the pseudo-elasticity appear in alloys which cause a thermo-elastic martensitic transformation. As for metallic materials showing such phenomena, there has been found mainly in a non-ferrous alloy such as Ti-49.about.51 at. % Ni, Ni-36.about.38 at. % Al, Cu-38.about.42 wt. % Zn, Cu-14 at. % Al-3.about.4.5 at. % Ni, Cu-15 at. % Sn, Au-46.about.50 at. % Cd and In-18.about.23 at. % Tl.
Contrary to this, it is found in a ferrous alloy that Fe-25 at. % Pt and Fe-30 at. % Pd become the thermoelastic martensite and show the complete shape memory effect. Further, it is briefly reported that Fe-23% Ni-10% Co-10% Ti alloy shows the shape memory effect by an aging treatment for one minute at 700.degree. C., but a relation between the shape memory effect and characteristics of martensite for this alloy is not clear. Moreover, it is further reported that Fe-high Nm alloys and Fe--Cr--Ni stainless steels such as 18-8 stainless steel indicate an incomplete and partial shape memory effect when .epsilon.-martensite is formed. However, since the shape memory effect in the ferrous alloys due to .epsilon.-martensite is incomplete, the application thereof is largely limited.
The complete shape memory effect and pseudo-elasticity originating from thermoelastic martensite are peculiar properties which do not appear in usual metallic materials, and thus various studies on this application are now continued. However, in actuality, there are three problems with this metallic material, i.e., a manufacturing problem such as melting, working, heat treatment; a problem of obtaining certain properties such as strength, ductility, toughness, fatigue life; and a problem of price.
Among the shape memory alloys mentioned above, Ti--Ni alloys, Cu--Zn alloys and Cu--Al--Ni alloys actually be used, but these alloys are not perfect and have various disadvantages. That is to say, Ti--Ni alloys have good properties, but they require a special technic during the manufacturing operation especially the melting operation and are very expensive. Contrary to this, Cu based alloys are comparatively inexpensive, but they have a poor workability during the manufacturing operation. In addition, they have a bad ductility and easily incur boundary cracks. These disadvantages of the Cu based alloys are the most fundamental problems that must be solved immediately.
Therefore, if the shape memory alloys having good properties for actual use are developed in the compositions other than those alloys mentioned above, it is possible to use this facility most effectively.